Phasic excitation of dopamine neurons in ventral VTA by noxious stimuli

TLDR

Midbrain dopamine neurons are key to reward processing, yet evidence suggests subgroups differ, particularly in how they encode aversive stimuli. The study aimed to test whether VTA dopamine neurons differ in coding for noxious stimuli by recording and labeling individual neurons in anesthetized rats. Researchers recorded and juxtacellularly labeled individual VTA dopamine neurons in anesthetized rats to link anatomical location and neurochemical identity with responses to noxious stimuli. Dorsal VTA dopamine neurons are inhibited by footshocks while ventral VTA neurons are phasically excited, revealing two anatomically and functionally distinct dopamine systems that reconcile prior contradictory observations.

Abstract

Midbrain dopamine neurons play central roles in reward processing. It is widely assumed that all dopamine neurons encode the same information. Some evidence, however, suggests functional differences between subgroups of dopamine neurons, particularly with respect to processing nonrewarding, aversive stimuli. To directly test this possibility, we recorded from and juxtacellularly labeled individual ventral tegmental area (VTA) dopamine neurons in anesthetized rats so that we could link precise anatomical position and neurochemical identity with coding for noxious stimuli. Here, we show that dopamine neurons in the dorsal VTA are inhibited by noxious footshocks, consistent with their role in reward processing. In contrast, we find that dopamine neurons in the ventral VTA are phasically excited by footshocks. This observation can explain a number of previously confusing findings that suggested a role for dopamine in processing both rewarding and aversive events. Taken together, our results indicate that there are 2 functionally and anatomically distinct VTA dopamine systems.